1. Field of the Invention
The invention relates to a caster for shopping and transport trolleys which are suitable for conveyance on travelators.
2. Description of Related Art
A caster of this type has been developed by the applicant under the designation “type III travelator caster”. This caster has a wheel fork provided with fork arms and carrying an axle body formed from square bar steel and extending through a hub arranged between the fork arms. Two running wheels intended for rolling along the floor are rotatably mounted on the hub, which has a circumferential crosspiece arranged between the two running wheels. The crosspiece is downwardly extended and forms a mounting for receiving a supporting means on which the caster is supported in a known manner when its running wheels are located in the grooves of the conveyor belt of a travelator. The supporting forces are transmitted via the hub to the axle body and from there to the wheel fork. The hub therefore has to be precisely positioned between the fork arms and secured against rotation so that the supporting means always points downwards. Rotational security is achieved by the use of the axle body formed from square bar steel. The axle body is therefore mounted in square openings in the fork arms. The hub likewise has an opening of square cross-section for receiving the axle body.
The endeavour is to keep the production costs for casters of this type as low as possible. These costs also include the assembly costs which are applicable when the individual components are assembled into finished casters. It therefore suggests itself to automate assembly processes of the type just described. In the present caster, such processes are relatively hard to achieve because the hub has to be inserted in a precise position between the fork arms owing to the downwardly extended mounting and also the square opening for receiving the axle body. Consequently, both the axle body manufactured from square bar steel and the above-described hub are unsuitable for automatic assembly.
German utility model DE 295 18 629 U1 also describes a caster for shopping and transport trolleys which are intended for conveyance on travelators. Two hub halves, on which two casters are rotatably mounted, are arranged between the fork arms of the wheel fork of this caster. A screw secured by a nut is provided as an axle body and extends through the two hub halves and the fork arms. A supporting foot is arranged on the outside of one of the two fork arms. The supporting foot carries a supporting means which has the same function as described in relation to the aforementioned caster.
The running wheels of the two casters just described, which form part of the prior art, are arranged at a mutual distance such that shopping and transport trolleys fitted with these casters are conveyable on travelators which conform at least to European standard EN 115. The running wheels of the casters extend into the grooves of the moving travelator belt so that the supporting means of the casters rest on the bridge pieces forming the grooves and the shopping and transport trolleys are maintained stationary on the travelator.
Owing to different methods of construction of the travelators, two difference distance measurements (spacings) for the aforementioned grooves have to be taken into consideration. A first spacing is 8.5 mm, the second spacing is 9 mm. This situation led in the past to the development of two types of caster in which the distance between the running wheels (gauge) was adapted to the two different spacings of the grooves. In a first type of caster the gauge formed by the running wheels is 25.5 mm (3×8.5 mm), and in the second type of caster it is 27 mm (3×9 mm). Different casters for the same purpose have to be stored separately and increase the risk of being mixed up or confused when the casters are replaced for repair purposes.